The first scientific report of the use of hybrid clays in the preparation of nanocomposites appeared in the U.S. Pat. No. 2,531,396, the disclosure of which is incorporated herein by reference. This patent, filed in 1947, describes the use of organically modified bentonites to provide structural reinforcement to elastomers such as rubber, polychloroprene and polyvinyl compounds. Several patents granted in 1984, for example U.S. Pat. Nos. 4,472,538; 4,739,007; 4,810,734; 4,889,885; and 5,091,462, the disclosures of which are incorporated herein by reference, use hybrid clays for plastics and describe the use of structural commercial plastics, for example, to replace steel components in automobiles.
Patents not related to nanocomposites have also been published describing hybrid clay compositions as technological additives that include the product of the reaction of clay, the cuaternary ammonium compound and the organic anions that are inserted in the clay, for example, U.S. Pat. No. 4,412,018, the disclosure of which is incorporated herein by reference, which uses a large variety of organic compounds, including carboxylic acids, that are capable of reacting with the quaternary ammonium.
The manufacture of nanocomposites also includes the mixture of hybrid clay with a powdered polymer, which is compressed to obtain a pellet while is heated at an appropriate temperature. For example polyestyrene has been intercalated by mixing polystyrene with montmorillonite modified with alkylammonium and heated in vacuum. The temperature is chosen in such a way that it is higher than the glass transition temperature of polystyrene in order to ensure the melting of the polymer.
U.S. Pat. No. 4,810,734, the disclosure of which is incorporated herein by reference, describes a different process for producing a nanocomposite that involves a contact step between a clay with a cation exchange capacity of 200 milliequivalents per 100 g with a swelling agent in a dispersing medium, forming a complex that has the property of swelling with the monomer (for example, an amino acid for a polyamide, vinyl chloride for vinyl polymers, among others) and then the monomer in the mixture is polymerized. The “swelling agent” used has an onium ion (for example, the ammonium, triethylammonium, trimethylphosphonium or dimethylsulfonium ions, among others) and a functional group (for example, a vinyl, carboxyl, hydroxyl, epoxy or amino group, among others) capable of reacting with the polymer. U.S. Pat. No. 4,889,885, the disclosure of which is incorporated herein by reference, describes a nanocomposite that comprises at least one resin chosen from the vinyl base polymer group, a thermostable resin and a rubber, and laminar bentonite uniformly dispersed in the resin. The laminar silicate has a layer thickness of approximately 7 to 12 nm, and an interlaminar distance of at least 30 nm, where the resin is connected with a silicate sheet by means of an intermediary.
There have also been several U.S. patent applications, among them U.S. Pat. Nos. 4,690,868 and 4,798,766, the disclosures of which are incorporated herein by reference, in which ammonium gas is used to modify smectic clays prior to preparing the nanocomposite.
Many of the products described in the aforementioned references cite that the products are easy to process and isolate, but are difficult to disperse in a polymer matrix.
Hybrid clays manufactured by intercalation of the quaternary ammonium salts are easy to isolate by filtering and washing because the clay acquires a more hydrophobic character. These materials, however, do not have good compatibility with certain plastic materials.
U.S. Pat. No. 5,552,469, the disclosure of which is incorporated herein by reference, describes the use of hybrid clay by intercalation in a water-soluble polymer, but there are problems in separating the modified clay from the aqueous phase. Isolation of the clay was possible from the aqueous solution at 100° C. This process leaves unintercalated polymer together with the intercalated clay, and therefore its isolation is not possible. A mixture of clay and monomer was subjected to polymerization forming a nanocomposite in situ in which the clay is well dispersed in the polymer. Unfortunately, this technique is a polymerization process of very high cost and it also produces contamination of the plant with clay.
Recent patents of invention since 1999, including U.S. Pat. No. 5,993,769; EP0952187; WO0044825; EP1055706; WO0166268; US2004087700; WO2006058846, the disclosures of which are incorporated herein by reference, have shown the interest in the development of nanocomposites using hybrid clays or clays intercalated with various synthetic and commercial organic compounds, and even some of natural origin, with the purpose of trying to optimize the compatibilization with polymer matrices in order to obtain nanocomposites.